First Biologic Therapy for Psoriasis That Can Be Self-Administered Once Weekly, at Home

South San Francisco and Berkeley, Calif. -- October 27, 2003 --

Genentech, Inc. (NYSE: DNA) and XOMA Ltd. (Nasdaq: XOMA) announced today that RAPTIVA (efalizumab) has been approved by the U.S. Food and Drug Administration (FDA) for the treatment of chronic moderate-to-severe plaque psoriasis in adults age 18 or older who are candidates for systemic therapy or phototherapy. RAPTIVA is the first biologic therapy that is designed to provide continuous control of chronic moderate-to-severe plaque psoriasis and can be self-administered by patients as a single, once-weekly, subcutaneous injection.

"Today's FDA approval of RAPTIVA underscores our commitment to delivering innovative therapies to patients with unmet medical needs," said Arthur D. Levinson, Ph.D., Genentech's chairman and chief executive officer. "Through our collaboration with XOMA, the clinical trial investigators and most importantly, the over 2,700 patients who participated in our clinical trials, we are proud to offer a new therapeutic option to help patients manage this chronic disease."

"RAPTIVA represents XOMA's first product approval and is the culmination of a highly successful collaboration with Genentech," said John L. Castello, XOMA's chairman, president and chief executive officer. "The companies have worked together on a robust clinical program that has demonstrated the safety and efficacy of RAPTIVA. We view RAPTIVA now being available to patients as a worthy testament to the confidence of our shareholders and the hard work and support of both companies' employees."

"I've been treating psoriasis for over 15 years and have always been frustrated by the limited options available to treat patients with this chronic disease. Safety limitations of traditional therapies have made it difficult to offer patients continuous relief," said Craig Leonardi, M.D., clinical associate professor of dermatology of Saint Louis University, St. Louis, Mo. and a RAPTIVA clinical investigator. "RAPTIVA has the potential to break the cycle of intermittent therapy by offering patients and their doctors a convenient treatment regimen that can be used continuously."

RAPTIVA is a humanized therapeutic antibody designed to selectively and reversibly block the activation, reactivation and trafficking of T-cells that lead to the development of psoriasis symptoms. In clinical studies, RAPTIVA demonstrated a rapid onset of action in the reduction of symptoms associated with psoriasis, in some patients within four weeks of initiating treatment. RAPTIVA is administered once weekly via subcutaneous injection and can be self-administered by patients at home.

"Since there is no cure for psoriasis, people have to manage their disease over their lifetime. It is a major challenge to find a treatment that works, has a favorable track record for safety and can be easily integrated into a patient's life," said Gail M. Zimmerman, president and chief executive officer of the National Psoriasis Foundation. "RAPTIVA offers a new treatment option for psoriasis that because of its convenience and ease of administration may provide patients with a sense of control over their disease."

Genentech and XOMA are collaborating on the development of RAPTIVA in the United States. Serono S.A., Genentech's marketing partner outside the United States and Japan, announced earlier in the year that it had submitted a Marketing Authorization Application (MAA) to the European Agency for the Evaluation of Medicinal Products (EMEA) for European Union Approval of RAPTIVA in psoriasis. Serono has also submitted RAPTIVA data for marketing approval in Canada, Switzerland, Australia and New Zealand and is filing in additional countries.

Clinical Trial Results
The Biologics License Application (BLA) submission included data on more than 2,700 patients treated with Raptiva, representing the largest existing database of patients treated with a biologic therapy for psoriasis.

The FDA's approval decision was based on data from four randomized, placebo-controlled Phase III studies. The Phase III trials were designed to evaluate the safety and efficacy of RAPTIVA in treating chronic moderate-to-severe plaque psoriasis. The studies had a primary efficacy endpoint of 75 percent improvement in the Psoriasis Area and Severity Index (PASI). The PASI is a composite score that takes into consideration both the fraction of body surface area affected and the nature and severity of the psoriatic changes within the affected regions (erythema, infiltration/plaque thickness and desquamation). Secondary endpoints for the Phase III studies included physician assessment and patient-reported outcomes.

RAPTIVA demonstrated efficacy and maintained response in most patients after 12 weeks of treatment. Sustained responses to RAPTIVA have also been observed in uncontrolled open-label extension treatment trials when patients received RAPTIVA without interruption for 24 weeks.

Common adverse events that occurred at least two percent more frequently in RAPTIVA patients than in placebo included headache, infection (mostly upper respiratory infections), chills, nausea, pain, myalgia (muscle pain), flu syndrome, fever, back pain, and acne. Five of these events (headache, chills, fever, nausea and myalgia) were predominantly acute adverse events and were principally seen following the first two injections of RAPTIVA. For the third and subsequent doses, the incidence of acute adverse events was similar between the RAPTIVA and placebo groups. Less than one percent of patients were discontinued from treatment due to acute adverse events.

RAPTIVA is an immunosuppressive agent and has the potential to increase the risk of infection and reactivate latent, chronic infections. Many immunosuppressive agents have the potential to increase the risk of malignancy. The role of RAPTIVA in the development of malignancies is not known. Serious adverse events occurring in clinical studies with RAPTIVA were serious infections (0.4 percent in RAPTIVA vs. 0.1 percent in placebo), malignancy (the overall incidence of malignancies of any kind was 1.8 per 100 patient-years for RAPTIVA-treated patients compared with 1.6 per 100 patient-years for placebo-treated patients), thrombocytopenia (0.3 percent RAPTIVA vs. 0.0 percent placebo), and worsening of psoriasis, typically upon discontinuation (0.7 percent in RAPTIVA vs. 0.0 percent in placebo).

About Psoriasis
Psoriasis occurs when new skin cell growth rapidly accelerates, resulting in thick, red, scaly, inflamed patches on the skin surface. Psoriasis affects approximately 4.5 million Americans. Plaque psoriasis, the most common form of the disease, is characterized by inflamed patches of skin ("lesions") topped with silvery white scales. Psoriasis can be limited to a few spots or involve extensive areas of the body, appearing most commonly on the scalp, knees, elbows and trunk. Although it is highly visible, psoriasis is not a contagious disease. While there are a number of medications that may help control the symptoms of psoriasis, there is currently no cure. For more information on psoriasis, log on to www.allaboutpsoriasis.com or visit the National Psoriasis Foundation's Web site at www.psoriasis.org.

For full prescribing information, visit www.gene.com or call 1-877-RAPTIVA. For more information on RAPTIVA including information on comprehensive support services, visit http://www.RAPTIVA.com or call 1-877-RAPTIVA.

About Genentech
Genentech is a leading biotechnology company that discovers, develops, manufactures and commercializes biotherapeutics for significant unmet medical needs. Sixteen of the currently approved biotechnology products originated from or are based on Genentech science. Genentech manufactures and commercializes 12 biotechnology products in the United States. The company has headquarters in South San Francisco, California and is traded on the New York Stock Exchange under the symbol DNA. For additional information about the company, please visit http://www.gene.com.

About XOMA
XOMA develops and manufactures antibody and other protein-based biopharmaceuticals for disease targets that include immunological and inflammatory disorders, cancer and infectious diseases. XOMA's programs include collaborations: with Genentech, Inc. on the RAPTIVA antibody for psoriasis (FDA approval), psoriatic arthritis (Phase II) and other indications; and with Millennium Pharmaceuticals, Inc. on a recombinant protein, CAB-2 for vascular inflammation (preclinical). Earlier-stage development programs focus on antibodies and other compounds developed by XOMA for the treatment of acne (Phase I), cancer and retinopathies. For more information about XOMA's pipeline and activities, please visit XOMA's website at http://www.xoma.com. .

Regarding XOMA:
Statements made in this news release related to the safety and efficacy of RAPTIVA, as well as the collaborative arrangements regarding RAPTIVA, or that otherwise relate to future periods, are forward looking statements within the meaning of Section 27A of the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934. These statements are based on assumptions that may not prove accurate. Actual results could differ materially from those anticipated due to certain risks inherent in the biotechnology industry and for companies engaged in the development of new products in a regulated market. These risks include those related to safety and efficacy of the product (including the product's ability to remain safe and efficacious in the long term); market acceptance of and demand for the product (including analysis and interpretation by physicians and others of scientific data); competition; changes in the status of existing collaborative relationships; the ability of collaborators to meet their obligations; and pricing of and reimbursement for the product. These risks are discussed in XOMA's most recent annual report on Form 10-K and in other SEC filings. Consider such risks carefully in evaluating XOMA's prospects.